This disclosure relates to rotors that have blades which are mounted in slots in a rotor disc. More particularly, the disclosure relates to the lay-up of composite layers in an area of blade attachment.
A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustor section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
Rotors, such as turbine rotors in gas turbine engines, typically include a disc that has axially extending slots around its periphery for mounting turbine blades. The slots have a “toothed” profile and each of the blades has a root with a corresponding profile to interlock with the toothed profile of the slots. In applications in which the blade is constructed from multiple layers forming a ceramic matrix composite, the root typically is provided by a simple dovetail geometry.
High Strength ceramic matrix composite (CMC) blades use uni-directional weaves and/or tapes because the layup can use radially biased fiber orientation with some dispersed angular aligned plies. This type of layup architecture is known to create a layup with substantially higher strength in the primary load direction, than a comparable 2D or 3D woven cloth layup. The planar layers of uni-directional weave also results in CMC components with substantially less through-thickness porosity than comparable CMC component made from 2D and 3D woven layups, due to the absence of tow-to-tow overlap within the layer/ply.
Stacked layups of uni-directional plies, due to their lower porosity and the absence of tow-to-tow overlap, demonstrate substantially higher through-thickness compressive Young's Modulus (sometimes referred to as “E33”) than layups created with 2D and 3D weaves. Blade attachments bearing surfaces experience high compressive loads due to the radial constraint imposed by the disk attachment. The compressive load distribution on the blade root is a function of the compressive compliance of the blade and disk features. If the load is unable to distribute over a large enough area, load concentration occurs, and local overstress may result in premature fracture of the blade root or disk attachment.
Typically, a CMC blade has very low porosity, for example, less than 5%. It has generally been desirable to process the CMC to reach a density that approaches the theoretical density of the material, that is, without voids or porosity. Historically, a compliant layer has been used to separate the CMC/ceramic blade from the metallic disk. Although successful, this thin layer has limited ability to distribute load through local compressive yielding. The limiting component remains to be the blade root region. One technique for mitigating stress is to secure metallic pads near the neck and fillet. Another technique for mitigating stress is to provide wedges that float with respect to the slot and the blade tooth.